A portable data- or signal-processing terminal includes a battery that must be recharged periodically from the power grid, or a cell, that must be changed. Considering, for example, a cellular radio unit, it consumes electrical energy even when it is on stand-by but unused, since it must remain partially fed in order to be located by the stations of the radio network. Due to this fact, the battery has limited autonomy.
The user of the unit therefore must find a compromise between tedious rechargings at short intervals, and not always necessary or even satisfactory on the electrical level, and the risk of disconnection through loss of energy since his unit had not been recharged for a long period of time.
In order to obtain a measurement of the consumption, and thus to warn the user of a need to recharge, since the current consumed from the battery is very variable, sampling the measurement of a current sensor could be contemplated at a sufficiently high rate in order to recreate its form and then to effect a digital filtering in order to smooth out the signal and obtain this measurement of consumption. However, such a solution would be complex.
The present invention seeks to measure, in a simpler manner, the current consumed by the circuits of a portable terminal.
To this effect, the invention concerns, first, a device for measurement of the current exchanged between an energy storage source and the electrical circuits of a portable data- or signal-processing terminal, comprising a current measurement sensor intended to be connected between the source and said circuits, characterized by the fact that the sensor is connected to a first input of a first integrating means, arranged so as to integrate the current measurement and to control, as a result, comparison means arranged so as to detect the crossing of a high threshold through the integral of the current and then to apply, to a second input of the first integrating means, a calibrated feedback signal to recall below the high threshold, and second integrating means are provided to integrate the feedback signals in order to provide a measurement of the current exchanged.
Thus, the first integrating means integrate the current and thereby perform a low-pass filtering on it, therefore becoming independent of the instantaneous values that can be assumed. They can have great sensitivity since the feedback limits the dynamics of operation at the high-threshold value. In other words, the comparison means reduce the integral of the current and the two integrating means make a cumulative total of the reductions, which represents the measurement sought, that is to say, the true integral (without feedback) of the current from the start of the measurement.
The invention also concerns a portable data- or signal-processing terminal, characterized by the fact that it includes a device in accordance with the invention.
The invention will be better understood with the aid of the following description of a preferred embodiment of a terminal including the measurement device of the invention, and of a variant, with reference to the attached drawings.